1. Field of the Invention
The present invention relates to a sewing needle holding unit for use in a sewing machine, wherein a sewing needle can be attached to the sewing needle holding unit with a high positional precision.
2. Description of the Related Art
There have been provided a variety of types of sewing machines, such as electric household sewing machines and industrial use sewing machines. Normally, sewing machines include a needle bar and a sewing needle holding unit attached to the lower end of the needle bar. A motor drives the needle bar to reciprocally move in the vertical direction. A sewing needle is detachably attached to the sewing needle holding unit. In this way, the sewing needle is also reciprocally moved in the vertical direction.
A loop taker is driven in conjunction with the vertical movement of the needle bar so that stitches can be formed by cooperative operation of the sewing needle and the loop taker.
One type of sewing needle holding unit is formed with a vertical hole in the under surface of its bottom end and a horizontal hole in its side. The horizontal hole extends to the vertical hole. In order to attach a sewing needle to the sewing needle holding unit, first, a head portion of the sewing needle is inserted into the vertical hole from below. The vertical hole is formed slightly larger than the outer periphery of the sewing needle head portion so as to facilitate insertion of the sewing needle. Then, a male screw is screwed into the horizontal hole until the tip of the male screw abuts against the sewing needle head portion. When the male screw is tightly screwed, the sewing needle is pressingly fixed in place within the vertical hole. The male screw is formed from a relatively soft material. This is because if the male screw is formed from a hard material, the male screw can easily break when rotated.
However, when the male screw is screwed into the horizontal hole while rotating, its rotational movement generates a great deal of friction between the tip of the male screw and the sewing needle head portion. Because the vertical hole is formed slightly larger than the outer periphery of the sewing needle head portion as described above, the friction slightly rotates the sewing needle within the vertical hole in the same direction as the rotation of the male screw. As a result, the sewing needle may be fixed in place with a slight tilt. Also, the sewing needle may be slightly lowered by rotation of the screw, resulting in fixing the sewing needle at a position slightly lower than desired.
When the sewing needle is inaccurately attached in this manner, an eye of the sewing needle is shifted from the accurate position. As a result, the loop taker beak of the loop taker may not accurately catch the upper thread loop extending from the eye of the sewing needle. This causes skipped stitches. Also, the sewing needle may be damaged by bumping against the loop taker.
Further, because the male screw is formed from the relatively soft material, the tip of the male screw easily deforms by pressing against the sewing needle. The deformed tip enters and catches onto the sewing needle. As a result, when the male screw is tightened, the sewing needle is further easily rotated. This results in fixing the sewing needle in place at an undesired position or orientation.
Japanese Utility Model Application Publication No. SHO-49-90359 discloses a different type of sewing needle holding unit. Specifically, the sewing needle holding unit includes a clasp supported within a lower end portion of the needle bar. Both the lower end portion of the needle bar and the clasp have a slightly V-shaped cross section. The clasp is formed with a screw hole. With this configuration, a sewing needle is first inserted into a predetermined space defined between the needle bar and the clasp. Then, a male screw is screwed into the screw hole. As a result, the clasp moves relative to the needle bar, so the sewing needle is pressed between the needle bar and the clasp. In this way, the sewing needle is pressingly fixed in place.
However, producing the needle bar with the V-shaped end portion requires precise metal work, resulting in complicating overall manufacture processes of the sewing machine. Also, manufacturing costs are increased because the clasp has a complicated shape and a relatively large size.
Japanese Utility Model Application Publication No. SHO-49-105361 discloses another type of sewing needle holding unit. Specifically, the sewing needle holding unit includes a needle mount and a judgement plate both supported by a lower portion of the needle bar. A sewing needle is first inserted into a predetermined space defined between the needle mount and the needle bar. By screwing a male screw into a hole formed in the needle mount, the needle mount moves relative to the needle bar. As a result, the sewing needle is pressingly fixed in place between the needle mount and the needle bar.
However, this configuration requires the needle mount of a relatively large size and a complicated shape, thereby increasing its manufacturing cost.
Japanese Patent Application-Publication No. SHO-59-37986 discloses another type of sewing needle holding unit. The sewing needle holding unit includes a needle mount. The needle mount is supported at a lower portion of the needle bar such that a space is formed between the needle mount and the needle bar. A spacer is slidably and pivotably supported within the space by a screw. A sewing needle is inserted between the spacer and the needle bar. When a male screw is screwed into a screw hole formed to the needle mount, the spacer is pushed toward the sewing needle. By tightly screwing the male screw, the sewing needle is fixed in place between the spacer and the needle bar.
However, complicated operations are required for attaching the spacer between the needle mount and the needle bar. Also, the needle bar needs to be processed so that the needle bar can support the spacer and the sewing needle. Further, the configuration of the sewing needle supporting unit is complicated.